The giant modular sarcomeric protein nebulin extends along the thin filaments in skeletal muscle and has important roles in various processes. Mutations in the nebulin gene account for about 50% of cases of the congenital neuromuscular disorder nemaline myopathy (NM). There is evidence to support a functional role for the nebulin C-terminal SH3 domain in the sarcomeric Z-disk, and now, Marie-Louise Bang, Ju Chen and colleagues (p. 5477) dissect this role using two approaches. They first sought to identify novel interaction partners of the nebulin SH3 domain using affinity-based proteomic screening and then generated a mouse line in which the nebulin SH3 domain is deleted (NebΔSH3 mice). Characterisation of the NebΔSH3 mice unexpectedly revealed no structural or histological abnormalities and no changes in gene expression or localisation of nebulin SH3 interaction partners. There was also no change in maximum isometric stress generation and passive load bearing in the muscle. NebΔSH3 muscle did, however, display slightly blunted sensitivity to electrical simulation at lower frequencies, and was more susceptible to eccentric contraction-induced injury compared with wild-type muscle. The authors conclude that, in contrast to what has previously been reported, the nebulin SH3 domain is dispensable for Z-disk assembly or maintenance, or for coordinating transcriptional responses in muscle, but it does seem to be necessary to maintain muscle contractility under especially under eccentric exercise conditions.